Mail app & third-party clients not showing Lock Screen notifications (IMAP custom)

Hi everyone,

I’m running into a persistent issue with Mail notifications not appearing on the Lock Screen, even though every setting is correctly configured and I’ve tested across multiple devices and apps.

Device & system

• iPhone 17 Pro (iOS 26.1)
• Tested also on a second iPhone – same result
• Mail account type: IMAP (custom domain – name@facembranduri.ro)
• Hosted on Hosterion (cPanel) – confirmed to support IMAP IDLE (push)

Symptoms

• Emails are received instantly and correctly in all apps (Mail, Gmail, Outlook).
• However, no Lock Screen notification is triggered when a new email arrives.
• No banner, no sound, and no preview. The badge count only updates after opening the app.
• The Mail app used to display instant notifications before.

What I have tested so far :

Mail app

• Allow Notifications: ON
• Lock Screen, Notification Center, Banners: ON
• Sounds: ON
• Badges: ON
• Show Previews: Always (Default)
• Notification Grouping: Automatic
• Focus / Do Not Disturb / Scheduled Summary: OFF
• Fetch New Data: Push enabled globally and for this specific account
• Tried both manual IMAP setup and configuration via profile (VPN/MDM)
• Rebooted multiple times
• Same result: emails are received, but no Lock Screen notification.

Outlook app

• All Notifications: ON
• Time-Sensitive Notifications: ON
• Lock Screen, Notification Center, Banners: ON
• Background App Refresh and Cellular Data: ON
• Focused Inbox: ON
• Tried both IMAP and Exchange-style setup (manual)
• Same result: messages arrive but no Lock Screen notification or sound.

Gmail app

• Notifications: All
• Works correctly only for native Gmail accounts.
• IMAP (custom domain) accounts receive emails but no push notifications, only periodic sync.

Additional information

• Mail server: mail.facembranduri.ro (Hosterion, Romania)
• IMAP Port 993 (SSL ON)
• SMTP Port 465 (SSL ON)
• DNS / MX records are correct; webmail works flawlessly.
• The issue is reproducible on multiple iPhones, even after clean configuration.
• No Apple Watch is paired (so notifications are not being redirected).

Question

Has Apple changed the way Mail handles push (IMAP IDLE) notifications for non-iCloud or non-Exchange accounts in iOS 20+?

Is this a known issue or limitation affecting IMAP push notifications on iOS 20+?

If so, is there any official workaround or fix planned in a future update?

I’m looking for a way to restore instant Lock Screen notifications for my business IMAP account (custom domain hosted on Hosterion).

Thank you in advance.